In an LTE (Long Term Evolution) mobile communication system, according to an Inbound handover procedure to a CSG (Closed Subscriber Group) cell, in order to solve problems caused by “PCI confusion” and perform a “preliminary access check”, a mobile station UE is configured to receive broadcast information transmitted in the cell of a handover destination (Target Cell), and transmit “CGI (Cell Global Identity)” of the cell of a handover destination, “TAI (Tracking Area Identity)” of the cell of a handover destination, or “member/non-member indication”, which indicates the belonging or non-belonging to “CSG-ID” broadcasted by the cell of a handover destination, to a radio base station S-eNB (Serving eNB) during communication.
Such an operation is called “SI (System Information) reporting”. In addition, according to a normal handover procedure, the “SI reporting” is not performed.
It is possible for the radio base station S-eNB to uniquely designate a radio base station T-eNB (Target eNB), which manages the cell of a handover destination, by using the CGI and the TAI notified by the “SI reporting”, and to transmit “HO Preparation signalling” to the radio base station T-eNB.
Furthermore, the radio base station S-eNB is configured to determine whether to perform a handover to the radio base station T-eNB of a mobile station UE or whether it is necessary to perform an “accessibility check” by a mobile switching center MME (Mobility Management Entity), based on the received “member/non-member indication”.
Here, when a “measurement report” is received from the mobile station UE, based on “PCI (Physical Cell Identity)” included in the received “measurement report”, the radio base station S-eNB is configured to determine whether there may occur “PCI confusion” in a cell with the PCI and whether it is necessary to perform a “preliminary access check”.
For example, the radio base station S-eNB may be configured to set the range of PCI used for a CSG cell/a hybrid cell/an open (macro) cell at the time of starting a network operation, to determine the type of the CSG cell/the hybrid cell/the open cell based on the above-described PCI, and to determine that it is necessary to perform the “preliminary access check” when a cell designated by the above-described PCI is the CSG cell/the hybrid cell.
Furthermore, when the cell designated by the above-described PCI is the CSG cell/the hybrid cell, the radio base station S-eNB may determine that there probably occurs the “PCI confusion”.
Furthermore, the radio base station S-eNB may classify the range of the PCI used for the open cell into the range of PCI used for a cell (for example, an open femto cell) where there may occur the “PCI confusion” and the range of PCI used for a cell (for example, a normal macro cell) where there is no probability of the “PCI confusion”, and may determine that it is necessary to solve problems caused by the “PCI confusion” when the PCI belonging to the former range is reported.
When it is determined that it is necessary to solve problems caused by the “preliminary access check” or the “PCI confusion”, it is possible for the radio base station S-eNB to transmit an “SI reporting request” for requesting the “SI reporting”, to the mobile station UE.
Here, the “SI reporting request” designates the PCI of a cell subject to “SI reporting”, to the mobile station UE.
When the “SI reporting request” is received, the mobile station UE is configured to receive SI, which has been broadcasted in a cell with the PCI designated by the “SI reporting request”, based on an “autonomous gap”, and to transmit CGI, TAI, or “member/non-member indication” included in the received SI, to the radio base station S-eNB.
That is, the mobile station UE is configured to temporarily interrupt the transmission/reception of a signal with a cell (a serving cell) during communication at a reception timing of SI (MIB and SIB1 in the case of an LTE scheme) broadcasted in the cell, and to receive the SI broadcasted in the cell.
Then, when succeeding the reception of the SI in a predetermined period (scheduled to be about 150 ms in the LTE scheme), the mobile station UE is configured to report necessary information to the radio base station S-eNB.
In addition, even when failing the reception of the SI in the predetermined period, the mobile station UE is configured to report the failure to the radio base station S-eNB.
Here, when the “SI reporting” is requested to a CSG cell that is not granted to access, the mobile station UE encounters, at each time, interruption of transmission/reception of a signal with a cell that is in communication, and signal transmission for the “SI reporting” or a C-plane process.
Therefore, when a large number of CSG cells that are not granted to access exist around the mobile station UE, the wasted “SI reporting” may frequently occur.
In order to solve such a problem, the mobile station UE is configured to transmit “proximity indication” based on an “autonomous search”.
That is, the mobile station UE holds fingerprint information of a CSG cell that is granted to access and upon detection that the mobile station UE approaches the CSG cell based on the fingerprint information, the mobile station UE is configured to transmit “entering proximity indication” to the radio base station S-eNB, and upon detection that the mobile station UE has been away from the CSG cell, the mobile station UE is configured to transmit “leaving proximity indication” to the radio base station S-eNB.
Here, the fingerprint information indicates surrounding environments of the CSG cell, and for example, may include a cell ID of a neighboring macro cell, RSRP (Reference Signal Received Power) of a neighboring cell, GPS information, and the like.
When the “entering proximity indication” is reported from the mobile station UE, it is possible for the radio base station S-eNB to transmit, as needed, the “SI reporting request” to PCI reported by a subsequent “measurement report”.
Consequently, the “SI reporting” is implemented only in an area designated by the fingerprint information, so that it is possible to avoid the implementation of waste “SI reporting”.
In addition, the “proximity indication” is used for the control of a “measurement configuration” for a cell having a different frequency or a different RAT (Radio Access Technology) cell, as well as the control of the “SI reporting”.
That is, if the “measurement configuration” for the cell having a frequency or RAT different from that of a cell that is in communication has not been set, it is not possible for the mobile station UE to perform “measurement” for the cell having a different frequency or the different RAT (Radio Access Technology) cell.
When the CSG cell that is granted to access exists with a frequency or RAT different from that of a cell that is in communication, around the cell that is in communication, the mobile station UE transmits the “entering proximity indication” to the radio base station S-eNB so as to enable requesting the setting of a necessary “measurement configuration”, and transmits the “leaving proximity indication” so as to enable requesting the deletion of an unnecessary “measurement configuration”.
The “measurement configuration” may include a “measurement object” indicating the cell having a frequency or RAT different from that of the cell that is in communication, a “reporting configuration”, “measurement identity”, a “measurement gap”, and the like.
To this end, it is possible for the mobile station UE to notify information on a frequency or RAT for requesting the “measurement configuration” through the “proximity indication”.
However, in current control in the above-described mobile communication system, when a number of CSG cells for which the mobile station UE has no access permission exist in an area designated by the fingerprint information, there is a problem that the “SI reporting” may frequently occur.
Furthermore, the setting of the fingerprint information depends on each case, and therefore, high accurate fingerprint information such as GPS information is not always set in the mobile station UE, and for example, the fingerprint information may be set in units of TAs or PLMNs (Public Land Mobile Networks).
In such a case, in the current control, there is a problem that the frequent occurrence of the “SI reporting” may not be sufficiently suppressed. SUMMARY OF THE INVENTION
Therefore, the present invention has been achieved in view of the above-described problems, and an object thereof is to provide a mobile communication method, a mobile station, and a radio base station, by which it is possible to suppress the frequent occurrence of waste “SI reporting”.
A first characteristic of the present embodiment is summarized in that a mobile communication method comprising, a step of transmitting, by a mobile station that is in communication in a cell of a first frequency, indication information including cell identification information used in a scrambling process for a synchronization signal broadcasted in a cell of a second frequency to a radio base station managing the cell of the first frequency, upon detection of entry of a predetermined area corresponding to the cell of the second frequency for which the mobile station has access permission or upon detection of exit from the predetermined area, a step of transmitting, by the mobile station, a measurement report including the cell identification information to the radio base station, and a step of reporting, by the mobile station, predetermined information broadcasted in the cell of the second frequency in response to a report request received from the radio base station.
A second characteristic of the present embodiment is summarized in that a mobile station, comprising, an indication information transmission unit configured to transmit indication information including cell identification information used in a scrambling process for a synchronization signal broadcasted in a cell of a second frequency to a radio base station managing a cell of a first frequency, upon detection of entry of a predetermined area corresponding to the cell of the second frequency for which the mobile station has access permission or upon detection of exit from the predetermined area, during communication in the cell of the first frequency, a measurement report transmission unit configured to transmit a measurement report including the cell identification information to the radio base station, and a broadcast information report transmission unit configured to report predetermined information broadcasted in the cell of the second frequency in response to a report request received from the radio base station.
A third characteristic of the present embodiment is summarized in that a radio base station managing a cell of a first frequency, comprising, an indication information reception unit configured to receive indication information including cell identification information used in a scrambling process for a synchronization signal broadcasted in a cell of a second frequency from a mobile station that is in communication in the cell of the first frequency detected to enter a predetermined area corresponding to the cell of the second frequency for which the mobile station has access permission or the mobile station detected to exit from the predetermined area, a measurement report reception unit configured to receive a measurement report including the cell identification information from the mobile station; and a report request transmission unit configured to transmit a report request for requesting a report of predetermined information broadcasted in the cell of the second frequency to the mobile station.
As described above, according to the present invention, it is possible to provide a mobile communication method, a mobile station, and a radio base station, by which it is possible to suppress the frequent occurrence of waste “SI reporting”.